A structure of a radio base station including a radio equipment controller (REC) and a radio equipment (RE), which are separated from each other, is disclosed in Patent Literature 1 and Non-Patent Literature 1. The REC and the RE are at least functionally separated from each other. The REC and the RE are connected to each other through an internal interface (communication interface) of the radio base station. The REC and the RE may be arranged so as to be physically spaced apart from each other. In a typical layout, the REC is arranged in a main building of a telecom carrier and the RE is arranged at a remote location near an antenna.
The REC is connected to an upper network (e.g., a core network of a telecom carrier). The REC plays a role in controlling and monitoring the entire radio base station and performing digital baseband signal processing. In this case, the digital baseband signal processing includes layer-2 signal processing and layer-1 (physical layer) signal processing. The layer-2 signal processing includes at least one of (i) data compression/de-compression, (ii) data encryption, (iii) addition/removal of a layer-2 header, (iv) data segmentation/concatenation, and (v) composition/decomposition of a transfer format by data multiplexing/de-multiplexing. In the case of E-UTRA, as a specific example, the layer-2 signal processing includes processing of Radio Link Control (RLC) and Media Access Control (MAC). The physical layer signal processing includes channel coding/decoding, modulation/demodulation, spreading/de-spreading, resource mapping, and generation of OFDM symbol data (baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT).
The RE plays a role in performing analog radio frequency (RF) signal processing, and provides an air interface to a mobile station. The analog radio frequency (RF) signal processing includes D/A conversion, A/D conversion, frequency up-conversion, frequency down-conversion, and amplification. The RE is also referred to as a remote radio head (RRH).
For example, in the case of a radio access network of a universal mobile telecommunications system (UMTS), the REC provides a connection to a radio network controller (RNC) using an Iub interface for sending and receiving user data (user plane data) and control data (control plane data). On the other hand, the RE provides a mobile station with an air interface called a Uu interface.
In the case of Evolved Universal Terrestrial Radio Access (E-UTRA), the REC provides a connection to an evolved packet core (EPC) using an S1 interface for sending and receiving user data and control data. On the other hand, the RE provides a mobile station with an air interface called an LTE-Uu interface.
As described above, the separated structure of the radio base station disclosed in Patent Literature 1 and Non-Patent Literature 1 is characterized in that a part that performs analog RF signal processing is separated as the RE. This separated structure makes it possible to flexibly and effectively deal with an increase and a change in the functions implemented in the radio base station. In addition, this separated structure makes it possible to easily deal with independent advancement of an analog RF technique and a digital baseband technique by separating the two techniques.